Generally speaking there are three reasons why movement in Unity will stutter.
- Viewing the game in the editor, not the standalone player
- Moving using...

...For example, when working in 2D, you may want to ignore the vertical movement of the camera, so that it follows the player along...

...would move the player 1.4 times faster than just moving forwards or sideways alone, causing uneven 8-way movement.
One method for fixing...

...s pointing at the player may, in some cases, be facing downwards at an angle.
This means that any movement that’s applied will...

...You’d usually use object-relative movement like this when allowing the player to control an object.
But how can you turn player input...

...example, can move the player 1.4 times faster than just moving forwards or sideways alone, causing faster diagonal movement.
So how can you...

...For example, will you use physics to launch the player upwards, or will you use script-based movement to manually move the character up...

...Which method you use is your choice, however, because this particular action (zooming in and out in first-person) is basically a player movement...

...For example, you might use one Action Map for general movement but, when the player jumps in a vehicle, you’ll want the same...

...relative movement in Unity, including how calculate camera direction and how to adjust for the camera’s height.
How to use the Player Input...